Facilitation of flicker discriminability by electrical stimulation of the mesencephalic reticular formation of the rat.

Abstract

Low-intensity, 7 and 10 /xA, electrical stimulation of the mesencephalic reticular formation (MRF) in seven rats significantly improved the accuracy of a perceptually difficult successive discrimination between a smooth light and a rapidly flickering light. Despite similar baseline conditions, including accuracy, MRF stimulation did not affect accuracy when the flickering light was maintained at an easily detectable 5 Hz. Accuracy of the perceptually difficult discrimination was not affected by changes in water deprivation or by electrical stimulation of the inferior colliculus or the fornical area of the limbic system. These findings suggest that the stimulation-induced improvement in the accuracy of the perceptually difficult flicker discrimination was not due to nonspecific changes in motivation, arousal, or general attention or to the possible cue or alerting function of the stimulation. The failure to implicate nonsensory processes and the finding that accuracy was improved only when the light was flickering rapidly indicate that MRF stimulation increased accuracy by improving the discriminability of the rapidly flickering light.Behavioral and electrophysiological evi-arousal has been extensively examined dence implicating the mesencephalic retic-since that time (e.g., Isaac, 1960; Vierck, ular formation (MRF) in the modulation of 1965); however, the equally promising hyboth arousal (Lindsley, Schreiner, pothesis that the MRF also modulates sen-Knowles, & Magoun, 1950; Morruzzi & sory processing has not received the same Magoun, 1949) and sensory processing experimental attention. The present ex- (Fuster, 1958;Lindsley, 1958) existed by periments reexamine this important hy-1958. The notion that the MRF mediates pothesis.Lindsley and Griffiths (cited in Lindsley, 1958) reported electrophysiological This research was supported in part by Grant evidence indicating that the MRF modu-F?i M Hi! 4 ? 6 r fr °m th f ^ational !? f tu « e °f *? en ; !ates the discrimination of a pair of light tal Health to George A. Heise and by Biomedical n L. c• i v -LA n i_ o -f Sciences Support Grant PHS RR 7031-10 to Indiana flashes from a sln i le h g ht flash -SpeClfl-University. The assistance of George A. Heise and cally, they found that in the acute cat or Richard A. Martin in preparing the manuscript and monkey, two 20-jU-Sec light flashes sepain constructing the apparatus is gratefully acknowlrate( J by 100 msec generated two distinct 6d Requests for reprints should be sent to John E. eV °ked Potentials in the visual cortex Kelsey, Department of Psychology, Indiana Uni-whereas a pair ot flashes separated by only versity, Bloomington, Indiana 47401. 50 msec generated a single merged poten-951 952 LEE HOYMAN AND JOHN E. KELSEY

Practice effects in backward masking.

“…When the reticular system of the monkeys was stimulated, however, two distinct evoked potentials were recorded with a 50-ms separation. Hoyman and Kelsey (1977) were concerned that the studies cited above had not ruled out general motivational explanations for the improvement effects and that no control animals were included who received stimulation of areas other than the reticular system. They controlled for these potential problems and examined the critical-flicker-fusion threshold in rats with stimulation in one of three sites: the reticular system, the inferior colliculus, or the limbic system.…”

Tactile discrimination following analgesia-producing brainstem stimulation in the rat

“…Second, the stimulation may have induced an internal state, such as arousal, positive hedonic effects, or aversive effects, which may have served as a distracter. However, strong behavioral reactions to stimulation that are suggestive of aversive effects of brainstem stimulation are associated with a generalized decrement in performance on all trials, not just on those with test stimulation (Frommer & Campos-Domingo, 1985), and arousal from midbrain reticular stimulation facilitates performance of sensory discrimination (Fuster & Uyeda, 1962;Hoyman & Kelsey, 1977). By itself, intense arousal due to strong motor effects of midbrain stimulation has no effect on errors in tactile discriminative performance during stimulation (Frommer & Campos-Domingo, 1985).…”